Method for determining an exhaust gas recirculation quantity for an internal combustion engine provided with exhaust gas recirculation

ABSTRACT

In a method of determining the quantity of exhaust gas recirculation for an internal combustion engine having exhaust gas recirculation, the exhaust gas recirculation quantity (r AGR , m AGR ) is determined from an exhaust gas temperature (T exhaust ), a fresh gas temperature (T air2 ), a fresh gas quantity (m air ) and/or a volumetric efficiency (η). The fresh gas temperature (T air2 ) is determined by a fresh gas temperature model ( 15 ) which is adaptively adjusted in response to influencing parameters relevant to the fresh gas temperature.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German patent document 102 42234.6, filed Sep. 12, 2002 (PCT International Application No.PCT/EP2003/009414, filed Aug. 26, 2003), the disclosure of which isexpressly incorporated by reference herein.

This invention relates to a method for determining an exhaust gasrecirculation quantity for an internal combustion engine, such as isused as a drive motor for motor a vehicle, for example.

Exhaust gas recirculation is known to offer advantages with regard tofuel consumption and exhaust emissions. The term “quantity” is used forthe sake of simplicity, to denote a physical variable indicative ofquantity (e.g., the mass or the quantity rate or mass flow rate) ofrecirculated exhaust gas and/or gas mixture fed into the internalcombustion engine.

The quantity of fresh gas fed into the combustion chamber(s) of aninternal combustion engine may be measured, for example, via a hot-filmmass flow meter (HFM) in a respective intake manifold and/or intakepath. The exhaust gas recirculation quantity cannot be determined inthis way, however, and is therefore conventionally determined (andknown) indirectly for at most a very specific design state, e.g., anormal state of an internal combustion engine without any additionalmeasures. For other engine operating states, and in particular forchanging temperatures and changing atmospheric pressure of theenvironment from which the fresh gas and/or fresh air for the motor isobtained, it is useful to establish a modified exhaust gas recirculationrate in comparison with the design state (i.e., the normal state), inorder to be able to comply accurately with emission limits, for example.Therefore there is a need to know exactly the exhaust gas recirculationrate at all points in time in order to be able to regulate it at asuitable level.

German Patent Document DE 199 34 508 A1 describes a method forcontrolling exhaust gas recirculation, wherein a setpoint exhaust gasrecirculation rate is determined on the basis of the engine load, enginetorque and air pressure; an actual exhaust gas recirculation rate andthe opening and closing movements of a throttle valve are detected bysensors, and an exhaust gas recirculation control valve is operated as afunction of the difference between the actual and setpoint exhaust gasrecirculation rates as well as a throttle valve opening signal, athrottle valve closing signal and the respective air pressure. Theexhaust gas recirculation quantity is determined by sensors based on ameasurement of the pressure difference at a throttle opening provided ina respective exhaust gas recirculation line.

U.S. Pat. No. 6,067,800 discloses the determination of the exhaust gasrecirculation quantity using an estimate of the fresh gas temperature asa function of influencing parameters.

A method for determining the exhaust gas recirculation quantity is knownfrom generic European Patent 1 221 544 A2, in which the exhaust gasrecirculation quantity is determined from an exhaust gas temperature, afresh gas temperature, a fresh gas quantity, and/or a volumetricefficiency, and the fresh gas temperature is determined by means of afresh gas temperature model that is adaptively adapted to influencingparameters relevant to the fresh gas temperature.

One object of the present invention is to provide a method of the typedefined in the preamble, which permits precise and reliabledetermination of the exhaust gas recirculation quantity with littleeffort, in particular at various operating states.

This and other objects and advantages are achieved by the methodaccording to the invention, in which the exhaust gas recirculationquantity is determined from an exhaust gas temperature, a fresh gastemperature, a fresh gas quantity and/or a volumetric efficiency. Thefresh gas temperature is determined by a fresh gas temperature modelwhich is adaptively adjusted while the engine is running, adapting it torelevant influencing parameters pertaining to the fresh gas temperature.Volumetric efficiency is a measure of the fresh gaseous supply to theengine. It is defined as the ratio of the total quantity of gas suppliedto the engine per operating cycle to the theoretical load, that is, theratio of the filling per operating cycle to the theoretical fresh loadin filling the geometric cubic capacity of the engine with air and/ormixture in the ambient state, when the engine is not supercharged and/orin the state downstream from a compressor and/or a charge air coolerthat is provided in an internal combustion engine with supercharging.For operation with exhaust gas recirculation, volumetric efficiency isdefined as the ratio of the total quantity of gas mixture supplied peroperating cycle to the quantity of gas mixture in filling the geometriccubic capacity of the internal combustion engine with gas mixture in thestate after admixture through the exhaust gas recirculation. Volumetricefficiency is also referred to as absorption capacity.

The exhaust gas temperature, a temperature of the recirculated exhaustgas (also known as the exhaust gas recirculation temperature), and thevolumetric efficiency are preferably also determined by correspondingmodels, which are adaptable to relevant influencing parameterspertaining to the respective quantities. Preferably, each of the modelscomprises a basic model, a correction model and/or a filter block. Withthe basic model, a basic value is determined for the output variableand/or for a part of the output variable of the corresponding overallmodel. This basic value is corrected, if necessary, by an outputvariable of the correction model if certain input variables that arerelevant for the output variable of the overall model deviate frompredefined reference values and/or reference states. When speaking of acorrection model, this in fact refers to a group of correction modelshaving one correction model per input variable. For the determination ofdeviations, the input variables are monitored, preferably by measurementand subsequent comparison with the reference values. The basic modelsand/or correction models are preferably engine characteristic mapsand/or characteristic lines, but they may also be linear and/ornonlinear mathematical and/or physical simulation models based ondifferential equations. The basic models and/or correction models mayalso be neural networks.

Each of the overall models preferably also has a filter block. Thefilter blocks are preferably first-order delay elements, so-called PT1elements. However, other filters, preferably dynamic filters, may alsobe used, such as delay elements of a higher order or delay elements incombination with monostable elements. By means of filtering, a dynamicresponse is imposed upon an input variable of a filter block, so that a(calculated) output variable of the filter block approximates the realresponse of the measured equivalent of the output variable. Suchfiltered variables, i.e., variables determined by filtering, can beadjusted and/or regulated more easily by a regulating and/or controllingmeans. This is the case with the exhaust gas recirculation rate inparticular. It is regulated more rapidly and has less overshooting,which leads to a lower component burden and to more steady emissions,thus preventing emission peaks. Filtering of variables is also known asdynamic correction.

The method according to the invention can be integrated to advantageinto a control unit, such as an engine control unit and/or a vehiclecontrol unit which is conventionally present in a motor vehicle, forexample. With the method according to the invention, the prevailingexhaust gas recirculation quantity (i.e., exhaust gas recirculationrate) can be calculated with a high precision under steady-state andnon-steady-state conditions and under different operating conditions andambient conditions.

The basic models and correction models are preferably determined inexperiments or on a test stand, for example, before market introductionof the internal combustion engine, and are stored in a memory of acontrol unit of the conventional type. The basic models and correctionmodels are preferably only type-specific, and are not determined inadvance for each individual internal combustion engine in this way andthen adapted to the individual engine during operation thereof.

The method according to the invention for determining the exhaust gasrecirculation quantity does not require any sensors for measuring theexhaust gas recirculation quantity. Even without exhaust gasrecirculation quantity sensors, the quantity of recirculated exhaust gascan be determined accurately and reliably. To do so, the models used areadapted by using certain correction models, so the method isautomatically adapted to changes occurring during the service life ofthe engine; such changes would include operating states that deviatefrom a basic state (e.g., non-steady-state processes, changes in ambientconditions).

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an internal combustion engine havingan intake path and an exhaust path;

FIG. 2 is a block diagram that illustrates the method according to theinvention, for determining the exhaust recirculation rate;

FIG. 3 is a block diagram of an overall model for determining a freshgas temperature;

FIG. 4 is a block diagram of an overall model for determining an exhaustgas temperature;

FIG. 5 is a block diagram of an overall model for determining atemperature of the recirculated exhaust gas; and

FIG. 6 shows a block diagram of an overall model for determiningvolumetric efficiency.

DETAILED DESCRIPTION OF THE DRAWINGS

The same reference notation is used here to denote the same functionalcomponents and/or quantities. For the sake of simplicity, certain inputvariables of certain function blocks such as summing points, filterblocks, models are identified with u. Likewise, certain output variablesof certain function blocks are indicated with y. The input variables andoutput variables have the reference notation of the correspondingfunction blocks as a subscript. If the input variables are referencevalues and/or reference states, also referred to as initial valuesand/or initial states, then these input variables have the numeral 0 asan additional subscript. If an input variable and/or an output variablestands for a group of input variables and/or output variables,respectively, then this input variable and/or output variable has theletter i as an additional subscript. The input variables and/or outputvariables may of course also be state variables and/or states. If afunction block is depicted as a rectangle having multiple rectanglesstaggered one behind the other, this is a depiction of a modelcomprising multiple individual models.

FIG. 1 is an example a system in which the inventive method may be usedfor determining an exhaust gas recirculation rate. An intake pipe and/oran intake path 4 for fresh gas and/or fresh air and an exhaust path 5are assigned to the internal combustion engine 1 having a driveshaft 2.A turbocharger 3 is provided in the intake path 4 and in the exhaustpath 5; a compressor of the exhaust gas turbocharger 3 is situated inthe intake path 4 and an exhaust turbine of the turbocharger 3 issituated in the exhaust path 5. An exhaust gas recirculation system 8 isprovided between the internal combustion engine 1 and the exhaust gasturbocharger 3, connecting the exhaust gas path 5 to the intake path 4.Downstream from the turbocharger 3 and upstream from the connectingpoint (not indicated further) to the recirculation system 8, a chargingair cooler 7 is preferably provided in the intake path 4. It is used forcooling the fresh air. Another cooler 9 and an exhaust gas recirculationvalve 10 are preferably provided in the recirculation system 8, with theexhaust gas recirculation valve preferably being situated downstreamfrom the charging air cooler 9.

A quantity of fuel m_(fuel) is supplied to the internal combustionengine through a feed line. In addition, a quantity of fresh gas mair issupplied to the internal combustion engine 1 through the intake path 4.This quantity of fresh gas m_(air) is measured by a sensor 6, e.g., ahot-film air-mass sensor (HFM). An exhaust gas quantity m_(exhaust) ispreferably sent through the exhaust path 5 into an exhaust system of thetype conventionally provided. The quantity of fresh gas is mixed with aquantity of exhaust recirculated through the recirculation system 8 at ameasurement point (not indicated further here) and is supplied as thegas mixture quantity m_(mix) to the internal combustion engine 1.

The temperature T_(air1) and the pressure of the fresh gas arepreferably determined (by appropriate sensors and meters) at ameasurement point 11 in the intake path 4 which is preferably situateddownstream from the charging air cooler 7 and upstream from theconnecting point to the recirculation system 8. In addition, variablesthat are also relevant for the inventive process include i) a fresh gastemperature T_(air2) at a point in the intake path 4 directly upstreamfrom the mixing point, (i.e., at a point 12), ii) for example, anexhaust temperature which corresponds to the temperature of the exhaustafter leaving the internal combustion engine at a point 13 in theexhaust path 5 and iii) a temperature of the recirculated exhaust whichcorresponds to the temperature of the recirculated exhaust preferablydirectly prior to admixture in the exhaust path 4. The method fordetermining the exhaust temperature and the temperature T_(Air2) isexplained in greater detail below.

FIG. 2 shows a block diagram of the inventive method for determining anexhaust gas recirculation quantity and/or an exhaust gas recirculationrate r_(AGR). In a function block 14, an exhaust gas recirculationquantity and/or an exhaust gas recirculation rate r_(AGR) is determinedfrom a temperature of a recirculated exhaust gas T_(AGR), hereinafteralso referred to as the exhaust gas recirculation temperature, a freshgas temperature and/or a charging air temperature T_(air2) directlybefore admixture of the added exhaust gas, a volumetric efficiency η andother input variables u_(14i) that are relevant in particular to theexhaust gas quantity and/or rate, in particular the fresh air quantitym_(air) determined via the sensor 6. This is done by using a massbalance equation, a volumetric efficiency equation which is based on theideal gas equation, and a mixing equation based on an energy balanceequation. In addition, a mixed temperature can be determined from thesevariables and equations after admixture of the recirculated exhaust gasin the intake path 4 and the total cylinder mass and/or gas mixturequantity m_(mix) drawn in by the internal combustion engine. The exhaustgas recirculation quantity m_(AGR) is determined by subtracting thefresh gas component m_(air) from the total gas mixture quantity m_(mix).

The fresh gas temperature directly before admixture of the recirculatedexhaust gas T_(air2) is calculated by means of a fresh gas temperaturemodel 15, based on the fresh gas temperature T_(air1) at the measurementpoint 11 (see FIG. 1) and additional input variables u_(15i) which arerelevant for the fresh gas temperature. The exhaust gas recirculationtemperature T_(AGR) is determined by means of an exhaust gasrecirculation model 17 from input variables u_(17i) which are relevantto the exhaust gas recirculation temperature and from the exhaust gastemperature T_(Exhaust), these in turn being determined by means of anexhaust gas temperature model 16 from input variables u_(16i) that arerelevant to the exhaust gas temperature. The volumetric efficiency η isdetermined by means of a volumetric efficiency model 18 from inputvariables u_(18i) which are relevant to the volumetric efficiency. Themodels 15 through 18 are illustrated in detail in FIGS. 3–6.

FIG. 3 shows a block diagram of the overall model for determining thefresh gas temperature T_(air2) and/or the fresh gas temperature model15. A fresh gas temperature T_(air2) directly before admixture of therecirculated exhaust gas is determined from the fresh gas temperatureT_(air1) at the measurement point 11 in FIG. 1, the fresh gas mass flowd_(mair)/dt and additional input variables u_(15.3i) that are relevantfor the fresh gas temperature. The input variables u_(15.3i) of thefunction block 15 of FIG. 2 comprise the fresh gas mass flow d_(mair)/dtand the input variables U_(15.3i). The model 15 describes heating orcooling of the fresh air intake and/or the fresh gas intake from thetemperature T_(air1) at the measurement point 11 up to a measurementpoint 12 directly prior to admixture of the recirculated exhaust gas inthe intake path 4. On the basis of the temperatures of variouscomponents, in particular the temperature of the internal combustionengine, there may be a significant heating, or in certain cases also acooling effect, which must be taken into account in determining theexhaust gas recirculation rate. The mass fraction of the fresh airand/or the fresh gas relative to the total quantity of gas mixture islarge in comparison with the recirculated exhaust gas, so an accurateknowledge of the temperature of the fresh gas immediately beforeadmixture of the recirculated exhaust gas is desirable. An inaccuratetemperature of the fresh gas would greatly distort the exhaust gasrecirculation rate calculated in the function block 14 in FIG. 2. Thefresh gas temperature model 15 thus describes the phenomenology of aheating process and/or a cooling process.

A basic temperature change y_(15.1) relative to a reference state and/oran initial state is determined from the fresh gas temperature T_(air1)and the fresh gas mass flow d_(mair)/dt, using a basic model 15.1 in theform of an engine characteristic map. In a correction model 15.3, acorrection variable y_(15.3i) for the change in the basic temperaturey_(15.3i) is determined from the fresh gas mass flow d_(mair)/dt andadditional input variables u_(15.3i). The deviation in the inputvariables u_(15.3i) from these respective predefined reference inputvariables and/or reference states u_(15.3i0) is taken into account here.This deviation is preferably defined as the difference between the inputvariables u_(15.3i) and the reference input variables u_(15.3i0)assigned to them. However, the deviation may also be defined as thequotient of the input variables u_(15.3i) and the reference inputvariables u_(15.3i0). The reference input variables u_(15.3i0) may beentered into a field 15.4, which is preferably a memory area of acontrol unit.

The input variables u_(15.3i) and the reference states u_(15.3i0)assigned to them preferably include a cooling water temperature of theinternal combustion engine and/or an ambient temperature. The correctionmodel 15.3 preferably involves a group of models for each input variableu_(15.3i). Likewise, the correction value y_(15.3i) is a vector and/or agroup of correction values, namely a correction value y_(15.3i) for eachinput variable u_(15.3i).

At a combining point 15.2, the correction value(s) y_(15.3i) is (are)added to the basic temperature y_(15.i). (A multiplication may also beperformed instead of a summation at the combining point 15.2.) Acorrected temperature change forms the output of the coupling point 15.2and is sent to a filter 15.5, which is preferably a first-order delayelement. A dynamic output variable (filtered and corrected temperaturechange) y_(15.5) is formed from the static input variable by means ofthe filter 15.5. Thus there is a dynamic correction. Due to thefiltering, the change in temperature preferably has a more fluid andthus more realistic course. At a coupling point 15.6, the filtered andcorrected temperature change y_(15.5) is added to the fresh gastemperature T_(air1) to form the fresh gas temperature immediatelybefore admixture of the recirculated exhaust gas T_(air2). Instead of asummation, a multiplication may also be performed at the coupling point15.6.

FIG. 4 shows a block diagram of the overall exhaust gas temperaturemodel 16 for determining the exhaust gas temperature T_(exhaust), basedon a fuel quantity m_(fuel), a rotational speed n of the internalcombustion engine and from additional input variables u_(16.3i) that arerelevant to the exhaust gas temperature T_(exhaust). In a basic model16.1, a basic temperature y_(16.1), preferably static, is determinedfrom the fuel quantity m_(fuel) and the rotational speed n. The inputvariables u_(16.i) of the function block 16 in FIG. 2 comprise the inputvariables u_(16.3i), the rotational speed n and the fuel quantitym_(fuel). Then a correction value y_(16.3i) for the preferably staticexhaust gas temperature y_(16.1) is determined from the input variablesu_(16.3i) in a correction model 16.3. To do so, any deviation of theinput variables u16.3 i from predefined reference input variables and/orinitial input variables u_(16.3i0) assigned to them is taken intoaccount in the correction model. This deviation is preferably defined asthe difference between the input variables u_(16.3i) and the referenceinput variables u_(16.3i0); however, it may also be defined as thequotient of these input variables. The reference input variablesu_(16.3i0) are determined in a basic reference variable enginecharacteristic map 16.4 to which the rotational speed n and the fuelquantity m_(fuel) are preferably supplied as input variables.

The input variables u_(16.3i) preferably include a cooling watertemperature of the internal combustion engine, a pressure and/or acharge pressure in the intake path 4 (e.g., at the measurement point 11in FIG. 1), a trigger start of injection (optionally a post-injection oran exhaust gas) back pressure, which varies greatly (especially whenusing a particulate filter in the exhaust gas path 5), a so-called railpressure, a temperature of the gas mixture in the intake path afteradmixture of the recirculated exhaust gas and before entrance into theinternal combustion engine and/or a mixed temperature from a previouscomputation step of the method according to the invention (preferablythe last computation step), and the exhaust gas recirculation rate froma previous computation step of the method according to the invention(preferably the last computation step). The rail pressure is understoodto be the pressure which prevails in diesel engines with a common raildevice on the common fuel supply line for the individual cylinders ofthe internal combustion engine. Except for the mixed temperature and theexhaust gas recirculation rate, the other input variables u_(16.3i) arepreferably in the form of measured values.

The method according to the invention takes place continuously. In otherwords, during operation of the internal combustion engine, the actualvalue for the exhaust gas recirculation rate is determined anew byrepeated iteration of the inventive method, and is thus updated. Themixed temperature (calculated in block 14 in FIG. 2) and the exhaust gasrecirculation rate (preferably that determined in the last computationstep and/or the last iteration of the inventive method) form the inputvariables u_(16.3i) of the correction model 16.3.

The correction model 16.3 includes a corresponding model (preferably anengine characteristic map) for each input variable u_(16.3i). Likewise acorrection variable y_(16.3i) is determined for each input variableu_(16.3i) by means of the correction model 16.3, which consists of agroup of models. The correction variable y_(16.3i) is thus a groupand/or a vector of correction variables which are added to thepreferably static basic exhaust gas temperature y_(16.1) at thecombining point 16.2, forming a corrected exhaust gas temperaturey_(16.2), preferably a static temperature. Instead of a summation, amultiplication may also be performed at the coupling point 16.2, if thisis advantageous. Thus a correction of the preferably static exhaust gastemperature value y_(16.1) takes place at the combining point 16.2 whenthe current operating state, as defined by the input variablesu_(16.3i), deviates from a reference state, as defined by the referenceinput variables u_(16.3i0).

The corrected, preferably static exhaust gas temperature y_(16.2) isfiltered (via a dynamic correction) in the function block 16.5, forminga current dynamic exhaust gas temperature T_(exhaust). Since there isusually a heat exchange of exhaust gas with an exhaust gas bend which istypically provided in a motor vehicle, the actual exhaust gastemperature differs from a statically determined exhaust gas temperaturey_(16.2). By filtering in the function block 16.5, the calculatedexhaust gas temperature can be approximated to the actual exhaust gastemperature.

FIG. 5 shows as a block diagram an overall model 17 (also referred to asthe exhaust gas recirculation model) for determining the temperature ofthe recirculated exhaust gas. The model corresponds in structure to thefresh gas temperature model 15. With the exhaust gas recirculation model17, the temperature of the recirculated exhaust gas T_(AGR) isdetermined from an exhaust gas temperature T_(exhaust) which representsthe output variable of the function block 16 (explained in greaterdetail with reference to FIG. 4), a mass flow of the recirculatedexhaust gas dm_(AGR)/dt (also referred to simply as the exhaust gasrecirculation mass flow), and additional input variables u_(17.3i) thatare relevant for the temperature of the recirculated exhaust gas. Theinput variables u_(17i) of the function block 17 in FIG. 2 include theexhaust gas recirculation mass flow dm_(AGR)/dt and the input variablesu_(17.3i). The exhaust gas recirculation model 17 is an overall modelfor the cooling of the recirculated gas by the cooler 9 of therecirculation system 8 (see FIG. 1) and includes an exhaust gasrecirculation cooler model.

In a basic model 17.1, a basic cooling y_(17.1) (corresponding to areference state u_(17.320)) is calculated from the exhaust gastemperature T_(exhaust) and the exhaust gas recirculation mass flowdm_(AGR)/dt. In a correction model 17.3, a correction variable y_(17.3i)for the cooling y_(17.1) is determined from the exhaust gasrecirculation mass flow dm_(AGR)/dt and the input variables u_(17.3i). Adeviation in the input variables u_(17.3i) from the reference variablesand/or initial input variables u_(17.3i0) is taken into account here bymeans of the correction model 17.3. This deviation is preferably definedas the difference between the input variables u_(17.3i) and thereference input variables u_(17.3i0). (Alternatively, it may also bedefined as the quotient of the input variables u_(17.3i) and thereference input variables u_(17.3i0).) The reference input variablesu_(17.3i0) are determined in advance, and preferably entered into afield 17.4 which is in turn saved in a memory area of a control unit.

The input variables u_(17.3i) preferably include a cooling watertemperature of the internal combustion engine and/or an ambienttemperature. The correction model 17.3 has a separate model for eachinput variable u_(17.3i), and thus comprises a group of correctionmodels. Likewise, one output variable y_(17.3i) of the correction model17.3 is assigned to each input variable u_(17.3i). The correction valueor values y_(17.3i) are added to the basic cooling y_(17.1) at acombining point 17.2, forming a corrected cooling y_(17.2). (Instead ofan addition, a multiplication may also be performed at the combiningpoint if this appears advantageous.) The corrected cooling y_(17.2) issubtracted from the current exhaust gas temperature at the combiningpoint 17.6, forming an exhaust gas temperature y_(17.6) that takes intoaccount cooling in the recirculation. The temperature variable y_(17.6)is sent to the filter block 17.5 for dynamic correction, to obtain arealistic characteristic in forming the exhaust gas recirculationtemperature T_(AGR). Due to the selected model structure of the exhaustgas recirculation model 17 and the input variables u_(17i) that are usedand are relevant for the exhaust gas recirculation temperature, it ispossible to reflect the phenomenology of a cooler provided in an exhaustgas recirculation line.

FIG. 6 shows a block diagram of an overall volumetric efficiency model18 for determining a volumetric efficiency η based on a fuel quantitym_(fuel), rotational speed of the internal combustion engine n and theinput variables u_(18.3i). The input variables u_(18.i) of the functionblock 18 of FIG. 2 include fuel quantity m_(fuel), rotational speed nand input variables u_(18.3i).

The fuel quantity m_(fuel) is filtered in a filter block 18.5, forming afiltered fuel quantity y_(18.5). The latter and the rotational speed nconstitute the input variables for a basic model 18.1 which is used fordetermining a basic volumetric efficiency y_(18.1). The basic model 18.1is preferably a volumetric efficiency engine characteristic map whichspans the rotational speed n and the fuel quantity m_(fuel), with thedependence on the rotational speed n being a flow effect and thedependence on the fuel quantity being a thermal effect. To bettersimulate this thermal effect, the fuel quantity m_(fuel) is filtered inthe filter block 18.5, preferably before being entered into the basicmodel 18.1. The filtering is preferably performed by a first-order delayelement. The basic volumetric efficiency y_(18.1) is corrected by acorrection value y_(18.3i) at a combining point 18.2. In forming thecorrection value or values y_(18.3i) the deviation in the inputvariables u_(18.3i) from the predefined reference states and/or initialstates and/or reference input variables u_(18.3i0) is taken intoaccount. This deviation is preferably defined as the difference betweenthe input variables u_(18.3i) and the initial variables u_(18.3i0). Thereference input variables u_(18.3i0) are preferably determined in areference variable model 18.4 which has the rotational speed n and thefuel quantity m_(fuel) as input variables. The reference variable model18.4 is preferably an engine characteristic map which covers the fuelquantity m_(fuel) and the rotational speed n.

The input variables u_(18.3i) preferably include the cooling watertemperature of the internal combustion engine and a mixed temperaturewhich has been determined in the function block 14 of FIG. 2 in aprevious computation step (preferably the latest computation step) ofthe inventive method. The mixed temperature is the temperature of thegas mixture after admixture of recirculated exhaust gas, but beforeentering the intake path 4 into the internal combustion engine. (SeeFIG. 1.) The mixed temperature as well as the cooling water temperatureconstitute a thermal influence of the volumetric efficiency because thevolumetric efficiency represents the ratio of the real quantity of freshgas in a cylinder of the internal combustion engine to the quantity offresh gas theoretically possible based on a reference location,preferably the mixing site of fresh gas, i.e., fresh air and recycledexhaust gas. The real quantity of gas mixture is influenced by the flowlosses between the mixing site and the cylinder, by heating and/orcooling of the gas mixture due to surrounding components. The heatingand/or cooling of the gas mixture due to the surrounding componentsleads to a loss of density or to an increase in density of the gasmixture.

The correction model 18.3 includes one model (or one enginecharacteristic map) per input variable u_(18.3i). Likewise, each inputvariable u_(18.3i) is assigned an output variable and/or a correctionvalue y_(18.3i). The correction value(s) y_(18.3i) is (are) added to thebasic volumetric efficiency y_(18.1) at a combining point 18.2, formingthe current volumetric efficiency η. The combining point 18.2 may alsobe a multiplication point if this appears advantageous.

In the volumetric efficiency model 18, the current volumetric efficiencyη is calculated on the basis of a basic volumetric efficiency y_(18.1).Alternatively, the current volumetric efficiency η can also becalculated on the basis of the volumetric efficiency equation mentionedabove

$\eta = \frac{m_{air} \cdot T \cdot R}{p \cdot v_{h}}$from the fresh gas quantity m_(air), the charging pressure p and thefresh gas temperature T as variables, where R is the individual gasconstant and V_(h) is the displacement of the internal combustionengine. The calculation methods are mathematically equivalent. Thecalculation starting from a basic volumetric efficiency offers theadvantage that only one value, namely the volumetric efficiency, need becorrected when there is a deviation from the reference state instead ofhaving to correct three values (pressure, temperature and fresh gasquantity).

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for determining exhaust gas recirculation quantity for aninternal combustion engine having exhaust gas recirculation wherein: theexhaust gas recirculation quantity is determined based on at least oneof an exhaust gas temperature, a fresh gas temperature, a fresh gasquantity, and a volumetric efficiency; the fresh gas temperature isdetermined using a fresh gas temperature model that is adaptivelyadjusted in response to influencing parameters relevant to the fresh gastemperature; at least one model for determining the variables fresh gastemperature, exhaust gas temperature, or volumetric efficiency comprisesa basic model which is used to determine a basic value, and a correctionmodel, which generates an output value that is used to correct the basicvalue when the values of variables relevant to the variable to bedetermined deviate from reference values of these variables.
 2. Themethod as claimed in claim 1, wherein the fresh gas temperature modelcomprises: a basic model which is used to determine a basic value for abasic temperature change; and a correction model which generates anoutput value that is used to correct the basic value when the values ofvariables relevant to the fresh gas temperature deviate from referencevalue of these variables.
 3. The method as claimed in claim 2, whereinat least a portion of a value determined for the fresh gas temperatureis filtered.
 4. The method as claimed in claim 1, wherein the exhaustgas temperature is determined by an adaptive exhaust gas temperaturemodel comprising a basic model which is used to determine a basic valuefor the exhaust gas temperature, and a correction model generates anoutput value that which is used to correct the basic value when thevalues of variables relevant to the exhaust gas temperature deviate fromreference values of these variables.
 5. The method as claimed in claim4, wherein at least a portion of a value determined for the exhaust gastemperature is filtered.
 6. The method as claimed in claim 1, wherein atemperature of the recirculated exhaust gas is determined from theexhaust gas temperature using an adaptive exhaust gas recirculationmodel comprising a basic model which is used to determine a basiccooling value, and a correction model which generates an output valuethat is used to correct the basic value when the values of variablesrelevant to the temperature of the recirculated exhaust gas deviate fromreference values of these variables.
 7. The method as claimed in claim6, wherein at least a portion of a temperature of the recirculatedexhaust gas is filtered.
 8. The method as claimed in claim 1, whereinvolumetric efficiency is determined using an adaptive volumetricefficiency model comprising a basic model which is used to determine abasic value for the volumetric efficiency, and a correction model whichgenerates an output value that is used to correct the basic value whenthe values of variables relevant to the volumetric efficiency deviatefrom reference values of these variables.
 9. The method as claimed inclaim 8, wherein a value that is determined for a fuel quantity isfiltered in the determination of the volumetric efficiency.